Earlier quoted context omitted.
Almost certainly due to bandwidth limitations on older versions of Thunderbolt. Full bit depth HDR 5k @ 120hz requires some absurd data thoughput.
I don’t think so. My M3 Pro is on the list as supporting 120 hz but it only has Thunderbolt 4. Also the base M4 doesn’t habe Thunderbolt 5 and it support 120 hz.
(Notice how they listed the M1 chips individually.)